tuning and unloading and stuff. I have Q's

[Jessica]

so, why do subs unload so easy below tuning, but not above tuning?

I mean, lest say you to to 5hz, would you see unloading at like 50hz or so? you tune to 50hz good luck playing 30hz right?

What manner of whitchcraft is going on here?

Just seems weird that the tuning is what helps cone control overall, all thing being equal and stuff, so it stands to reason, just cause we see 20hz as a lower freq than 50, doesnt mean the port sees that.

So, experts chime in, and if you want to speculate and dont know, chime in as well. Lets talk.

[reedal]

Oooo I'm in for this one. Excellent question. I love learning threads.

[Triticum Agricolam]

When you get much below tuning its like the box isn't even there, air can move freely through the port and your sub starts to act like its in free air, which is why your cone excursion starts to go through the roof.

Much above tuning its the opposite, the air cannot change direction and move through the port fast enough so your sub starts to act like the port isn't even there and the box is sealed. This is why once you get high enough above the tuning frequency the performance between a ported box and a sealed box of equal size is pretty much the same. Also at higher frequencies your output isn't limited by cone excursion but instead by the thermal capacity of the sub.

There are some really great animated gifs that shows how a speaker and port interact, I'll see if I can find them.

[Jessica]

When you get much below tuning its like the box isn't even there, air can move freely through the port and your sub starts to act like its in free air, which is why your cone excursion starts to go through the roof.

Much above tuning its the opposite, the air cannot change direction and move through the port fast enough so your sub starts to act like the port isn't even there and the box is sealed. This is why once you get high enough above the tuning frequency the performance between a ported box and a sealed box of equal size is pretty much the same. Also at higher frequencies your output isn't limited by cone excursion but instead by the thermal capacity of the sub.

There are some really great animated gifs that shows how a speaker and port interact, I'll see if I can find them.

so its like the subs are in a way too big sealed enclosure?

[Triticum Agricolam]

Found it, I copy and pasted the below from here: http://www.hometheaterhifi.com/volume_5_2/cmilleressayporting.html

Above Resonance

The air mass provided by the box volume and the port, or the passive radiator, can't react instantly to the pressure induced by the active speaker. Above its own resonant frequency, it's too slow (upper bandwidth limited) to suck any energy off the active driver, and it does almost nothing at all, refusing to move when the direction of force changes too rapidly. This is shown by the animation below. (For all three of the animations shown, the driver on top is active, while the driver on the bottom represents air in the port, or a passive radiator. The pendulum bar in between the two drivers represents air within the enclosure.)

At Resonance

As the active driver approaches the tuned frequency of the secondary resonant device, that device begins to actually suck energy so forcefully through the internal air pressure, that it loads the active driver. It uses the cone as the fulcrum to bear the force of its own acceleration, thereby limiting the active driver's excursion, and transferring the greater output to its own opening or surface.

Below Resonance

Below resonance, the reflex system backs off on loading the active driver, yet still moves quite a bit. But since it is merely venting the back-pressure instead of "cracking the whip," it's no more than a hole in the baffle, which causes cancellation with the active driver’s front output. Because of this, the output rolls off very steeply, at 24 dB per octave (over 200 times less output per halving of frequency.) Also, since the port does not limit excursion and the suspension force that would have been provided by the compliance of air in a sealed system doesn't exist because of the hole in the enclosure, the active driver can very easily bottom out, or smack itself into itself, below that tuned frequency.

I should note that one can't simply punch a hole in a sealed enclosure, put a pipe of whatever length will fit, and have a bass reflex enclosure that will yield a flat response. The output of the port and the driver at roll-off must be shaped so that they can be added correctly. Because the Q values of the reflex system and the active driver determine the shape of their response, in order to change from a sealed to a ported design, or vice versa, the cabinet, driver, or both must change.

ETA: The above explain and illustrates what's going on so much better than I did. The image for what happens at the resonant frequency shows why there is very little cone excursion at the tuning frequency.

[reedal]

Nice. I'll have to save this for future use.